444 Dr. A. C. Stokes on some 



the previously described Vorttcellce has such an apparent 

 twisting of this covering been noted. One border only of 

 the sheath seems to be conspicuously thickened, the spiral 

 line visibly crossing the pedicle and forming a curve on the 

 opposite side, thus producing the twisted aspect. The other 

 margin of the sheath is not distinguishable from the thread 

 when the pedicle is extended, and is apparently then in con- 

 tact with it. 



The body is quite changeable in shape ; the usual alteration, 

 besides shortening and widening, is the formation of a 

 deep depression in one side anteriorly, in this habit somewhat 

 resembling Vorticella smaragdina, Stokes*, in which this is 

 usually a conspicuous feature. 



As this is the eighth member of the genus found in Ame- 

 rican waters, and presumably restricted to this continent, the 

 event has been commemorated by compelling the long- 

 stemmed infusorian to bear the ordinal number as its specific 

 title. 



Urostyla trichogaster, sp. nov. (PI. XV. fig. 3.) 



Body elongate, elliptical, soft, and flexible, three times as 

 long as broad, both extremities rounded, somewhat narrowed 

 anteriorly, and slightly curved towards the left-hand side ; 

 upper lip prominent, crescentic ; the entire cuticular surface 

 roughened by minute elevations in irregularly longitudinal 

 clusters ; peristome-field obovate or subtriangular, extending 

 obliquely backward from the left-hand side of the frontal 

 border towards the right, to somewhat beyond the anterior 

 third of the ventral surface, bearing on the left-hand margin 

 a fringe of large, strong, adoral cirri and a row of fine paroral 

 cilia, the right-hand border supporting a conspicuous undu- 

 lating membrane and a row of preoral cilia, a series of long 

 fine endoral cilia depending from the median part and con- 

 tinued through the long, narrow, tubular pharynx ; the frontal 

 region between the right-hand side of the peristome-field and 

 the body-margin beset by numerous uncinate styles, gradu- 

 ally decreasing in size posteriorly, but suddenly passing into 

 the fine seta? which clothe the entire ventral surface in closely 

 approximated longitudinal lines; marginal setse uninterrupted, 

 longest on the posterior border ; anal styles slender, subequal, 

 ten to twelve in number, arranged in an oblique row, not 

 projecting beyond the body-margin ; contractile vesicle single, 

 spherical, on the left-hand side of the peristome near its pos- 

 terior extremity; nucleus single, subspherical, posteriorly 



* ' American Naturalist,' 1885, p. 18. 



